1. Field of the Invention
The present invention relates to an apparatus for successively taking out a plurality of objects stacked randomly using an industrial robot.
2. Description of Related Art
In taking out randomly staked objects such as workpieces one by one by a robot by detecting the objects using a visual sensor, there is a difficulty in how to treat objects overlapped with each other. This problem is generally solved by finding out an object located at the uppermost position in the stack of objects and taking out the uppermost workpiece.
In a method of detecting an interference of articles as disclosed in JP 9-91441A, it is determined whether or not there is any article other than a detected article in a circumferential region thereof using an image of articles captured by a TV camera, and overlapping of the detected workpiece and the other workpiece is determined based on an areas of the image of the other workpiece in the circumferential region and a height of the other workpiece determined by the other method. In this interference detection method, if the object of detection has a planner simple shape, for example, the detection of the other object will be vague to lower reliability of detection of the interference of the articles. Further, since the method other than the image processing is required for obtaining the height of the other article, this method is disadvantageous in manufacturing cost.
In an apparatus for recognizing position of an object as disclosed in JP 8-271223A, an object is detected by tracing an outline of an image of the object and if it is determined that there is overlapping of the object with other object, upper/lower positional relation of the detected object and the other object is determined based on a distribution of gradation of the overlapped portion of the image of the objects, or a height of the other object determined by emission of a reference light. In this apparatus, the determination of the overlapping of the objects depends on the tracing of the outline of the image of the objects, and it is highly probable that the outline of the image of the objects is not continuous because of reflecting condition of illuminating light on the objects, to lower reliability of the determination of the overlapped portion. Also, reliability of determination of the upper/lower position of the objects based on the distribution of gradation would be low for the same reason, and the emission of the reference light is disadvantageous in manufacturing cost of the apparatus.
Further, in an overlapping state recognizing method as disclosed in JP 9-53915A, an overlapped portion of detected objects is found out based on relative positions of the detected objects and upper/lower position of the objects is determined by judging what object the overlapped portion belongs to by local matching of features of the objects in the overlapped portion. In this method, the overlapped portion of the objects is determined by considering correlation of shapes of the objects geometrically. The processing for the determination would be simple in the case where each object has a simple shape such as a circle having a circumference at the same distance from a center of the shape, but if the objects have complicated shapes, processing for the determination will be complicated to increase calculation cost for carrying out the complicated processing.